1. Field of the Invention
The present invention relates to a dielectric resonator, an inductor, a capacitor, a dielectric filter, and an oscillator which are produced by forming a slot line in an electrode on a dielectric substrate, and a communication device using the above.
2. Description of the Related Art
Microstrip line resonators and slot line resonators are known types of resonators employing dielectric substrates for use in a microwave band or a millimeter wave band.
A conventional slot line resonator is a single resonator constructed using a linear slot line having a length of half a wavelength. Since the slot line resonator has continuous electrodes surrounding slots, electromagnetic energy is highly efficiently enclosed in the vicinity of the slot line resonator. Therefore, when the slot line resonator is implemented in a high-frequency circuit, less interference with other circuits occurs.
FIGS. 19A and 19B will be used to describe the conductor loss in a resonator using a conventional slot line. FIG. 19A is a cross-sectional view of the slot line. FIG. 19B is an enlarged view of the portion designated xe2x80x9cBxe2x80x9d in FIG. 19A. A slot line resonator has a certain amount of conductor loss.
The electrode, which constitutes the slots, is divided into three regions, i.e., an edge region, a top face region, and a bottom face region. Computation of the conductor loss is performed on each region using a simulator. The following Table 1 shows the ratio of the conductor loss in the top and bottom face regions of the electrode to the total conductor loss in a slot line in which the sizes shown in FIG. 19A are employed.
Regardless of the slot width, the loss in the top and bottom face regions of the electrode is the major portion of the total conductor loss. When, for example, the slot width is 100 xcexcm, approximately ninety percent of the total loss occurs at the top and bottom faces of the electrode.
Although dielectric loss occurs in the slot line resonator, the conductor loss is the dominant factor.
As described above, the conductor loss at the top and bottom faces of the electrode, caused by the so-called xe2x80x9cskin effectxe2x80x9d, provides the major portion of the total conductor loss The skin effect occurs because of a nonuniform distribution of current inside the electrode; in other words, because of greater current density at the surface of the electrode.
In response to these issues, the present invention is able to provide a dielectric filter, an inductor, a capacitor, and an oscillator in which conductor loss due to the skin effect is effectively reduced and a dielectric resonator having a high unloaded Q-factor (Q0), as well as a communication device using the above.
To this end, according to a first aspect of the present invention, there is provided a dielectric resonator including a slot line constructed by providing a slot electrode having a spiral slot on an external face of a dielectric layer or inside of the dielectric layer and a shield conductor provided at a predetermined distance from the slot electrode. The slot line is employed as a resonant line.
Hereinafter, an end of the spiral at the outermost circumference thereof is denoted an exterior end while an end of the spiral at the innermost circumference thereof is denoted an interior end. FIG. 17 shows the electromagnetic field distribution in a linear slot line and directions of the currents induced by the magnetic field. Broken curved lines represent the direction of the magnetic field, solid curved lines represent that of the electric field, and linear arrows represent that of currents in the slot electrode induced by electromagnetic waves propagating in the slot. A remarkable point is that the directions of currents flowing through the electrode on the respective sides of the slot are mutually opposite. The present invention constructively takes advantage of this effect. That is, by forming the slot line into a spiral shape, currents flowing through the electrode between neighboring turns of the spiral slot are counterbalanced whereby conductor loss is reduced.
In a typical slot line, one end thereof is a short-circuit end and the other end thereof is an open end. In this case, it is preferable that the line length be xcexg/2 or xcexg/4 when the resonant wavelength of the resonator is denoted as xcexg. Since the direction of the magnetic field is unchanged in a section between nodes of a standing wave in the resonator, the direction of the current induced in the slot electrode is also unchanged in that section. When the directions of the currents through the electrode on both sides of the entire slot are unchanged, by forming spiraled slots, the current counterbalance always occurs between neighboring turns. When a node of the standing wave exists in the resonator, by forming spiraled slots, there is a part in which the current density is increased. Therefore, it is preferable that the resonator (the slot) length be xcexg/2 or xcexg/4.
The width of the slot line may be wider in the proximity of the short-circuit end thereof than in the proximity of the open end thereof. The current density of the electrode on both sides is maximum at the short-circuit end thereof and zero at the open end thereof. By forming spiraled slots, since the turns of the slots where the current density is different are disposed closely, though the counterbalance occurs, the current counterbalance effect does not cause the current value to be zero. Accordingly, it is preferable that the slot width be gradually changed so that the current counterbalance occurs over the entire slot, whereby, as a result, the current value approaches zero.
In the dielectric resonator, the width of the slot line may be changed through substantially the entire length thereof. Furthermore, the width of the slot line may be changed by forming curves at certain positions along the longitudinal direction thereof.
In the dielectric resonator, one end of the slot line may be a short-circuit end and the other end thereof may be an open end, thereby employing the slot line as a quarter-wavelength resonant line. Because of this, the entire line length becomes shorter and the area occupied by the slot line is also further reduced.
In the dielectric resonator, when an exterior circumferential end of the slot line is a spiral short-circuit end, the slot line may be employed either as a quarter-wavelength resonant line or a half-wavelength resonant line. That is, the quarter-wavelength resonant line is obtained in a case where the interior end is an open end, while the half-wavelength resonator line is obtained in a case where the interior end is a short-circuit end. Both cases place the maximum value of the magnetic field intensity at the exterior end of the spiral slot line.
In the dielectric resonator, the slot electrode may have two spiral slots whose exterior circumferences are connected to each other having substantially a point-symmetry relationship therebetween and the interior circumferential ends of the two slots are individually employed as short-circuit ends of the slot lines.
Since this construction places at the symmetry point a maximum electric field value and places maximum magnetic field values at each of the interior ends of the two spiral slot lines individually, the electromagnetic field is highly efficiently enclosed.
In the dielectric resonator, the slot electrode may have two spiral slots whose exterior circumferences are connected to each other so as to have a line-symmetry relationship therebetween and the interior circumferential ends of the two slots are individually employed as short-circuit ends of the slot line. This construction places a maximum electric field value at the position on the symmetry line, and makes the distance between neighboring slot lines wider.
In the dielectric resonator, the slot may have a spiral shape obtained by deforming the entire body thereof substantially into a rectangle, which can reduce the area occupied by the spiral slot on the dielectric substrate.
According to a second aspect of the present invention, there is provided an inductor including a slot line constructed by providing a slot electrode having a spiral slot at one of an external face of a dielectric layer and inside of the dielectric layer, and a shielding conductor provided at a predetermined distance from the slot electrode. In the inductor, an end of the slot line is a short-circuit end and the length of the slot is not more than one-eighth of a transmission wavelength of the slot line.
In the inductor, the width of the slot line may be wider in the proximity of a short-circuit end thereof than in the proximity of an open end thereof, which makes the current density distribution in the longitudinal direction of the slot line uniform, whereby the total conductor loss is reduced.
According to a third aspect of the present invention, there is provided a capacitor including a slot line constructed by providing a slot electrode having a spiral slot at one of an external face of a dielectric layer and inside of the dielectric layer, and a shielding conductor provided at a predetermined distance from the slot electrode. In the capacitor, an end of the slot line is an open end and the length of the slot is not more than one-eighth of a transmission wavelength of the slot line.
In the capacitor, the width of the slot line may be wider in the proximity of a short-circuit end thereof than in the proximity of an open end thereof, which makes the current density distribution in the longitudinal direction of the slot line uniform, whereby the total conductor loss is reduced.
According to a fourth aspect of the present invention, there is provided a dielectric filter including a signal input/output unit and any one of the above dielectric resonators.
According to a fifth aspect of the present invention, there is provided an oscillator including a negative resistance circuit and any one of the above dielectric resonators. In the oscillator, the negative resistance circuit and the dielectric resonator are coupled.
According to a fifth aspect of the present invention, there is provided a communication device including at least one of the above described inductor, the above described capacitor, the above described dielectric filter, and the above described oscillator.
Other features and advantages of the invention will be understood from the following description of embodiments thereof, with reference to the drawings, in which like references denote like elements and parts.